U.S. patent number 6,489,862 [Application Number 09/678,954] was granted by the patent office on 2002-12-03 for method for reducing noise generated in a power amplifier.
This patent grant is currently assigned to Agilent Technologies, Inc.. Invention is credited to Michael L. Frank.
United States Patent |
6,489,862 |
Frank |
December 3, 2002 |
Method for reducing noise generated in a power amplifier
Abstract
Receive band filtering between the last two stages of an N-stage
power amplifier can reduce the R.sub.x band noise. There are N-1
interstage matching networks interposing N stage amplifiers, where
N.gtoreq.2. The interstage matching networks and stage amplifiers
are electrically connected in series. The N-1.sup.th interstage
matching network includes a receive band reject filter positioned
proximate to the output of the N-1.sup.th stage power
amplifier.
Inventors: |
Frank; Michael L. (Los Gatos,
CA) |
Assignee: |
Agilent Technologies, Inc.
(Palo Alto, CA)
|
Family
ID: |
24725013 |
Appl.
No.: |
09/678,954 |
Filed: |
October 3, 2000 |
Current U.S.
Class: |
333/187; 330/302;
330/306; 330/310; 333/189; 455/78 |
Current CPC
Class: |
H03F
3/1935 (20130101); H03F 1/56 (20130101); H03F
1/26 (20130101); H03F 2200/372 (20130101); H03F
2200/294 (20130101) |
Current International
Class: |
H03F
1/26 (20060101); H03F 3/193 (20060101); H03F
1/56 (20060101); H03F 3/189 (20060101); H03F
1/00 (20060101); H03F 003/68 (); H03F 003/24 ();
H03H 009/00 (); H03H 009/54 () |
Field of
Search: |
;333/124,133,187,32,189
;330/302,306,310 ;455/78,73 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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|
0862266 |
|
Nov 1997 |
|
EP |
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4-306922 |
|
Oct 1992 |
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JP |
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2000-138546 |
|
May 2000 |
|
JP |
|
WO 96/42134 |
|
Dec 1996 |
|
WO |
|
WO0024124 |
|
Apr 2000 |
|
WO |
|
Primary Examiner: Pascal; Robert
Assistant Examiner: Summons; Barbara
Claims
I claim:
1. A power amplifier comprising: a series of N stage amplifiers,
where N>2; a series of N-1 interstage networks interposing the
series of N stage amplifiers, wherein the series of N-1 interstage
networks and series of N stage amplifiers are electrically
connected in series; and wherein the N-1.sup.th interstage network
includes a receive band reject filter positioned proximate to the
output of the N-1.sup.th stage amplifier.
2. A power amplifier, as defined in claim 1, wherein the receive
band reject filter is selected from a group that includes surface
acoustic wave filters, film bulk acoustic resonators filters,
ceramic filters, and piezo-electric based filters.
3. A power amplifier, as defined in claim 1, wherein the N-1.sup.th
interstage network has an input impedance that approximates the
output impedance of the N-1.sup.th stage amplifier and has an
output impedance that approximates the input impedance of the
N.sup.th stage amplifier.
4. A power amplifier, as defined in claim 3, wherein the receive
band reject filter has an impedance that is between the output
impedance of the N-1.sup.th stage amplifier and The input impedance
of the N.sup.th stage amplifier.
5. A power amplifier, as defined in claim 4, the receive band
reject filter further comprising: a first film bulk acoustic
resonator connected between the input of the Nth stage amplifier
and the output of the N-1.sup.th stage amplifier; a second film
bulk acoustic resonator connected to the input; a first inductor
connecting between the second film bulk acoustic resonator and
ground; a third film bulk acoustic resonator connected to the
output of the N-1.sup.th stage amplifier; and a second inductor
connecting between the third film bulk acoustic resonator and
ground.
6. A power amplifier, as defined in claim 4, the receive band
reject filter further comprising: a first film bulk acoustic
resonator connected to the input of the Nth stage amplifier; two
paths, connected between the first film bulk acoustic resonator and
ground, each path including a film bulk acoustic resonator serially
connected to an inductor; and a second film bulk acoustic resonator
connected between the first film bulk acoustic resonator and the
output of the N-1.sup.th stage amplifier.
7. A power amplifier, as defined in claim 4, the receive band
reject filter further comprising: a first film bulk acoustic
resonator connected to the input of the Nth stage amplifier; a film
bulk acoustic resonator serially connected to an inductor,
connected between the first film bulk acoustic resonator and
ground; and a second film bulk acoustic resonator connected between
the first film bulk acoustic resonator and the output of the
N-1.sup.th stage amplifier.
8. A power amplifier, as defined in claim 1, wherein the receive
band reject filter is selected from a group that includes film bulk
acoustic resonator filters, ceramic filters, and piezo-electric
based filters.
9. A power amplifier, as defined in claim 1, wherein the receive
band reject filter comprises a plurality of film bulk acoustic
resonators.
10. A power amplifier comprising: a series of N stage amplifiers,
where N.gtoreq.2; a series of N-1 interstage networks interposing
the series of N stage amplifiers, wherein the series of N-1
interstage networks and series of N stage amplifiers are
electrically connected in series; and wherein the N-1th interstage
network includes a receive band reject filter positioned proximate
to the output of the N-1th stage amplifier, the receive band reject
filter comprising: a first film bulk acoustic resonator connected
between the input of the Nth stage amplifier and the output of the
N-1th stage amplifier; a second film bulk acoustic resonator
connected to the input; a first inductor connecting between the
second film bulk acoustic resonator and ground; a third film bulk
acoustic resonator connected to the output of the N-1th stage
amplifier; and a second inductor connecting between the third film
bulk acoustic resonator and ground.
11. The power amplifier of claim 10, wherein the N-1.sup.th
interstage network has an input impedance that approximates the
output impedance of the N-1.sup.th stage amplifier and has an
output impedance that approximates the input impedance of the
N.sup.th stage amplifier.
12. The power amplifier of claim 11, wherein the receive band
reject filter has an impedance that is between the output impedance
of the N-1.sup.th stage amplifier and the input impedance of the
N.sup.th stage amplifier.
13. A power amplifier comprising: a series of N stage amplifiers,
where N.gtoreq.2; a series of N-1 interstage networks interposing
the series of N stage amplifiers, wherein the series of N-1
interstage networks and series of N stage amplifiers are
electrically connected in series; and wherein the N-1th interstage
network includes a receive band reject filter comprising: a first
film bulk acoustic resonator connected to the input of the Nth
stage amplifier; two paths, connected between the first film bulk
acoustic resonator and ground, each path including a film bulk
acoustic resonator serially connected to an inductor; and a second
film bulk acoustic resonator connected between the first film bulk
acoustic resonator and the output of the N-1.sup.th stage
amplifier.
14. The power amplifier of claim 13, wherein the N-1.sup.th
interstage network has an input impedance that approximates the
output impedance of the N-1.sup.th stage amplifier and has an
output impedance that approximates the input impedance of the
N.sup.th stage amplifier.
15. The power amplifier of claim 14, wherein the receive band
reject filter has an impedance that is between the output impedance
of the N-1.sup.th stage amplifier and the input impedance of the
N.sup.th stage amplifier.
16. A power amplifier comprising: a series of N stage amplifiers,
where N.gtoreq.2; a series of N-1 interstage networks interposing
the series of N stage amplifiers, wherein the series of N-1
interstage networks and series of N stage amplifiers are
electrically connected in series; and wherein the N-1.sup.th
interstage network includes a receive band reject filter positioned
proximate to the output of the N-1 th stage amplifier, the receive
band reject filter comprising: a first film bulk acoustic resonator
connected to the input of the Nth stage amplifier; a film bulk
acoustic resonator serially connected to an inductor, connected
between the first film bulk acoustic resonator and ground; and a
second film bulk acoustic resonator connected between the first
film bulk acoustic resonator and the output of the N-1.sup.th stage
amplifier.
17. The power amplifier of claim 16, wherein the N-1.sup.th
interstage network has an input impedance that approximates the
output impedance of the N-1.sup.th stage amplifier and has an
output impedance that approximates the input impedance of the
N.sup.th stage amplifier.
18. The power amplifier of claim 17, wherein the receive band
reject filter has an impedance that is between the output impedance
of the N-1.sup.th stage amplifier and the input impedance of the
N.sup.th stage amplifier.
19. A power amplifier comprising: a series of N stage amplifiers,
where N.gtoreq.2; a series of N-1 interstage networks interposing
the series of N stage amplifiers, wherein the series of N-1
interstage networks and series of N stage amplifiers are
electrically connected in series; and wherein the N-1.sup.th
interstage network includes a receive band reject filter positioned
proximate to the output of the N-1.sup.th stage amplifier, the
receive band reject filter comprising a plurality of film bulk
acoustic resonators.
Description
FIELD OF THE INVENTION
The invention is related to the field of power amplifiers,
particularly towards noise reduction in the power amplifiers.
BACKGROUND
In a full duplex transceiver, both the transmitter and the receiver
can operate simultaneously. This results in two forms of
interference. The first interference is the T.sub.x (transmit) band
power getting into the receiver. The second interference is noise
generated in the R.sub.x (Receive) band by the T.sub.x portion of
the radio, and leaking into the R.sub.x portion of the transceiver.
Both types of interference are mitigated by using a duplexer. In
this instance, a duplexer is a three port, passive element
consisting of a pair of bandpass filters and supporting components.
One filter passes the T.sub.x frequencies and rejects the R.sub.x,
the other passes the R.sub.x and rejects the T.sub.x.
As the transmit (T.sub.x) power is not completely blocked by the
duplexer, the power can enter the receiver thus causing distortion.
In a filter-based duplexer, this is a measure of how well the
receive (R.sub.x) filter rejects the transmit T.sub.x band power.
The T.sub.x filter has no effect because the leakage is in the
pass-band of the T.sub.x filter.
The second interference is caused by noise in the R.sub.x band,
generated by the T.sub.x circuitry getting by the duplexer into the
receiver. This causes a loss of sensitivity. In a filter-based
duplexer, this is a measure of how well the T.sub.x filter can
reject the R.sub.x band power. The R.sub.x filter has no effect
upon this leakage because it is in the pass-band of the R.sub.x
filter. This type of crosstalk drives the design of the T.sub.x
chain. The sensitivity required of the receiver dictates how much
leakage is acceptable. The rejection of the duplexer dictates how
much noise power the T.sub.x chain can be allowed to generate.
The noise figure of an amplifier is a sum of all of its noise
sources, referenced to the input of the amplifier. The noise power
at the output of that amplifier is the sum of the gain of the
amplifier and the noise figure. Since the sensitivity required by
the R.sub.x branch of the transceiver is set, the allowable noise
power out of the T.sub.x branch effectively sets the maximum gain
of the power amplifier.
In full duplex handsets, there is another constraint. The gain
setting routine discussed above relies upon the R.sub.x noise at
the input to the power amplifier be at or near the noise floor
available at that temperature. The noise generated in the T.sub.x
chain previous to the power amplifier must be sufficiently rejected
to not increase the noise power at the output of the power
amplifier. This is accomplished by inserting a R.sub.x band reject
filter just in front of the power amplifier, in the T.sub.x band
signal path. The difficulty of building this type of R.sub.x
rejection filter is such that many handsets rely upon two filters
in parallel, each filter dealing with half the signal bandwidth,
adding half the pass-band to the reject band frequency. This makes
each filter of the pair much easier than a full band
implementation. The input signal is routed through a switch, then
into one of the filter pair. After the filter, the signal is then
recombined with a switch.
One prior art implementation, shown in FIG. 1, includes a R.sub.x
rejection filter in front of a two-stage power amplifier. Given
that this node is at or near the noise floor, and given the amount
of noise generated in the power amplifier, the amount of R.sub.x
rejection required in the duplexer can be specified. The duplexer
filter that implements the required rejection has an associated
insertion loss. This loss is in the T.sub.x band, and is dependent
upon the R.sub.x band rejection. Hence, the more rejection
required, the higher the loss in the T.sub.x band.
Since the power output of the handset is constant, higher loss in
the duplexer requires more power out of the power amplifier. At the
high power levels required, higher power requires more current,
thus, reducing battery life.
SUMMARY
Receive band filtering between the last two stages of an N-stage
power amplifier can reduce the R.sub.x band noise. There are N-1
interstage matching networks interposing N stage amplifiers, where
N greater than or equal to 2. The interstage matching networks and
stage amplifiers are electrically connected in series. The
N-1.sup.th or ultimate interstage matching network includes a
T.sub.x band filter positioned proximate to the output of the
penultimate or N-1.sup.th stage power amplifier.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates a functional block diagram for a full duplex
transceiver of the prior art.
FIG. 2 illustrates a functional block diagram for a full duplex
transceiver of the present invention.
FIG. 3 illustrates a functional block diagram for a power amplifier
using a prior art interstage matching network.
FIG. 4 illustrates a functional block diagram for a power
amplifier/filter 24 shown in FIG. 2.
FIG. 5 illustrates an interstage matching network of the present
invention shown in FIG. 4.
FIG. 6 illustrates noise reduction for a two-stage power amplifier
using a receive band reject filter in the interstage matching
network.
FIG. 7 illustrates another preferred embodiment of the interstage
matching network shown in FIG. 4.
FIG. 8 illustrates another preferred embodiment of the interstage
matching network shown in FIG. 4.
DETAILED DESCRIPTION OF THE DRAWINGS
In the present invention, the R.sub.x band noise dependency upon
the T.sub.x chain is reduced so that the duplexer rejection
requirement may be relaxed. As the loss is less, less power is
required from the power amplifier. This is turn requires less
current and results in longer battery life.
Filtering between the two stages of the power amplifier can reduce
the R.sub.x band noise. In particular, either a band reject or a
bandpass filter that rejects the R.sub.x band will reduce the noise
power. FIG. 2 illustrates a transceiver 10 using an N-stage power
amplifier of the present invention, where N.gtoreq.2. An antenna 12
is connected to a duplexer 14. The duplexer 14 receives data from
antenna 12 and transmits it to low noise amplifier (LNA) 16. A
receive R.sub.x filter 18 is connected between LNA 16 and a
downconverter 20. An IF filter 22 receives the output of
downconverter 20. The duplexer 12 transmits data received from a
power amplifier/filter 24. A transmit T.sub.x filter 26 connects
between power amplifier/filter 24 and an upconverter 28.
FIG. 3 illustrates a two-stage amplifier of the prior art. The
interstage matching network is an RLC network.
FIG. 4 illustrates a novel power amplifier/filter 24, as shown in
FIG. 2. While a two-stage power amplifier is illustrated, this
concept as will be described is easily extended to cover a N-stage
power amplifier. In this illustration, N equals 2. There are N-1
interstage matching networks interposing N stage amplifiers. The
interstage matching networks and stage amplifiers are serially
connected. The N-1.sup.th interstage matching network includes a
receive band filter positioned proximate to the output of the
N-1.sup.th stage power amplifier.
The N-1.sup.th interstage matching network has very low impedance.
The receive band filter is designed to operate at the required
impedance. The illustrative filter operates in a 6.OMEGA. network.
Approximately, 10 dB of net rejection results in about 10 dB
reduction in the output R.sub.x band noise power. The receive band
filter may be a surface acoustic wave filter, a film bulk acoustic
resonator (FBAR) filter, a ceramic filter, or a piezo-electric
based filter.
FIG. 5 illustrates a preferred embodiment of the interstage
matching network shown in FIG. 4. A first FBAR 52 is serially
connected between the input and a first inductor 54 is tied to
ground. A second FBAR 56 is connected between the input and output.
A third FBAR 58 is connected between the output and a second
inductor 60 that is tied to ground. The first and third FBARS 52,
58 have one resonant frequency while the second FBAR 56 has another
resonant frequency.
FIG. 6 shows the noise reduction for a two stage power amplifier
using the receive band filter shown in FIG. 4 in the N-1.sup.th
interstage matching network.
FIG. 7 illustrates another preferred embodiment of the interstage
matching network shown in FIG. 4. At node A, a first FBAR 30 is
connected between the input and second FBAR 32 that is connected to
the output. A third and a fourth FBAR 34, 36 are connected to node
A. An inductor 38 is connected between the third FBAR 34 and
ground. Another inductor 40 is connected between the fourth FBAR 36
and ground. The first and second FBARS 30, 32 have one resonant
frequency while the third and fourth FBARS 34, 36 have a different
resonant frequency.
FIG. 8 illustrates another preferred embodiment of the interstage
matching network shown in FIG. 4. At node A, a first FBAR 42 is
connected between the input and second FBAR 44 that is connected to
the output. Between node A and ground, a third FBAR 46 is serially
connected to an inductor 48. The first and second FBARs 42, 44 have
one resonant frequency while the third FBAR 46 has a different
resonant frequency.
* * * * *